In a printer, a copier, a scanner or other imaging system, paper or other media is loaded as a stack of cut sheets. A sheet is moved from the stack of media into the imaging region so that it can be printed, scanned, copied, or otherwise processed. A variety of rollers, for example, can be used to move the sheet from the stack into the imaging region. A roller that contacts a sheet in the stack of media is sometimes called the pick-up roller. The pick-up roller has a surface having sufficient friction with the sheet that when the pick-up roller is rotated, it causes the sheet to begin to move from the stack of media.
Power for rotating the pick-up roller can be supplied in a variety of ways, for example by a belt or by a gear train. The motor providing the power can be a dedicated motor for rotating the pick-up roller. In order to save the cost of additional motors, in some printing systems the motor powering the pick-up roller is shared with other functions in the imaging system, such as other portions of the media handling subsystem, or even for other more diverse functions of the imaging system, such as the maintenance station of an inkjet printer, as is described in U.S. Pat. Nos. 5,831,644; 5,971,520; 6,846,060; 7,225,697; and in commonly-assigned U.S. patent application Ser. Nos. 11/969,277 and 11/969,265.
There are different styles of pick-up assemblies. In some printers the pick-up roller(s) is/are mounted on a shaft that is fixed to the opposite sides of the printer. In other printers, a pick-up roller is mounted near one end of a pick arm that is pivotally mounted near the other end of the pick arm. A prior art example of a pivotable pick-up assembly 40, as described in commonly-assigned U.S. patent application Ser. No. 12/178,849 is shown in FIG. 1. Pick-up roller 320 is rotationally mounted on roller axle 46 near an end of pick arm frame 41. Near the other end of pick arm frame 41, drive gear 42 is mounted on axle, whose axis is coincident with the pivot axis of pick-up assembly 40. Drive gear 42 receives power from a motor (not shown), and transmits the power through axle 43 and gear train 45 to pick-up roller 320. Optionally, a torsion spring 44 provides a torque to cause the pivotable pick-up assembly 40 to rotate about its pivot axis so that the surface of the pick-up roller 320 is forced into contact with a sheet of a stack of media.
If power is supplied to a pivotable pick arm at the pivot mount end, and if the power is transmitted along the pick arm by a gear train to a pick-up roller at the other end, in some circumstances the gears of the gear train can bind, grind or lock up, causing noise or even damage to the gears. In particular, for printers or other imaging systems having a compact design, but capable of holding a relatively large stack of media, the length of the pick arm is not much larger than the maximum media stack height. In such cases, the range of angles of the pick arm with respect to the plane of the media stack, as the stack height goes from maximum to minimum, can include angles where forces on the pick arm inhibit free rotation of the gear train.
Furthermore, in a compact design printer or other imaging system, the space occupied by the gear train can compete with space needed for other components. Finally, in systems where the pick-up roller is driven by a motor having multiple functions, initiation of printing can be delayed if the motor is otherwise engaged and cannot therefore immediately move the next sheet of paper from the stack of media. This can slow down printing throughput.
What is needed is a power source and power transmission arrangement for driving a pivotable pick-up assembly consistent with compact imaging system design, reliable operation, low cost, and fast throughput.